Polyetheretherketone (PEEK), successfully developed and commercialized first by Imperial Chemical Industries, Ltd., England, has been used widely in many high-tech fields owing to its excellent comprehensive property. However, PEEK material itself has many disadvantageous: rapid drop in material modulus at high temperature caused by the low glass transition temperature and low application temperature (application temperature for long, ≦240° C.) caused by the low melting point, which greatly limit the range of application. In order to further raise the application temperature of polyaryletherketone material which is a critical material for reforming conventional industry, thereby satisfying the increasing demands on the heat resistance in advanced technical field, such as new energy, nuclear technology, space development, ocean engineering and the like. Many attempts have been made by the scientific research personnels. Firstly, PEEK has been blended with other high-performance materials such as polysulfone (PSF), polyether sulfone (PES), Polyimide (PAI), polyether amide (PEI), polyphenylene sulfide (PPS), polyetherketone (PEK) and so on to obtain a composite material. But phase separation exists in these composite materials and influences the mechanical performance and application of the materials. Next, a stiff structure has been introduced into the main chain of PAEK and the glass transition temperature (Tg) and melting point (Tm) have been raised so as to raise the application temperature of PAEK. New sorts of polymers, such as polyetheretherketoneketone (PEEKK), polyetherdiphenyletherketone (PEDEK), and polyetherdiphenyletherketoneketone (PEDEKK) have been presented in succession to satisfy the urgent needs of some sophisticated techniques. However, the difficulties in processing grow up with the continual increase in Tg and Tm. Recently, the Tm of a new sort of PAEK, developed successfully by the inventors, has reached 469° C., see reference 1 (Zhou H. W., Chen C. H., Wu Z. W. et al., Polymer Preprints [J], 1999, 40(1):203-204) and reference 2 (Zhou H. W., Doctoral Dissertation (Jilin Univ), 1999 “Research on the molecular design and chain structure of PAEK and the structure of condensed phase”). The PAEK material having a very high melting point, theoretically having the application temperature rasied up to 350° C., thus it is very difficult to be put into practice. The most major reason lies in the fact that it is very difficult to form this material into a practicable product. So the method of raising the Tg and Tm of PAIK to raise the application temperature has an obvious disadvantage. In addition, an attempt has been made to introduce a cross-linking point into the PAEK material thereby forming a cross-linked structure to obtain a high-performance material. But a degradation reaction takes place at the selected cross-linking point during the cross-linking reaction and causes the deterioration of the material performance. As a result, the desired result is not achieved.
Polymer materials can be classified into two types: thermoplastic materials and thermosetting materials. These two types of materials respectively have respective strong and weak points: the former has excellent processability and low application temperature, and the latter has high application temperature but is somewhat difficult to be formed into a cast piece having fixed dimension and shape. It is desired to develop a material exhibiting excellent material performances and processing properties by combining the excellent processability of the thermoplastic material with the excellent heat performance of the thermosetting material. It is the hot spot of research and development for the next generation material exhibiting high performance.
Therefore, in respect to the molecular design of PAEK, the strong points of the two types of materials are considered to combine into one material so that both the excellent processability of the thermoplastic material and the excellent heat resistance of the thermosetting material are fully utilized. Based on this design, the present inventors incorporated the thioether structure, which is capable of being subjected to a cross-linking reaction at high temperature or radiation conditions, into the main chain of PAEK as a cross-linking point. No degradation reaction takes place and no small molecules are produced during the cross-linking reaction. After a cross-linked network structure is formed, a high-performance thermosetting material having stable polymer molecular structure and performance can be obtained. In the process of preparation, the segment length between adjacent cross-linking points is made to be basically the same by regulating and controlling the regular distribution of the thioether structure in the PAEK segments by way of block copolymerization. In this way, the uniform distribution of the cross-linking points in the polymer segments is achieved. In addition, a series of controllable cross-linking PAEK can be prepared by changing the ratio of monomers in the polymerization process, to regulate and control the content of thioether structure in polymer segment. The mol percent is controlled in the range of 2.5%-30%. The material performance can be controlled and regulated by controlling and regulating the cross-linking density so as to achieve the object of controlling the material performance of the cross-linked PAEK and satisfying the different application requirements. Combining the excellent characteristics of the thermoplastic and thermosetting resin matrix, without increasing production cost, not only can solve the problem of low heat resistance of thermoplastic resin matrix but also can avoid the disadvantage of poor processability of thermosetting resin matrix. The material can be used at a temperature up to 350° C. It is great significant to develop a PAEK material with improved performance.